Both the advantage and disadvantage between two kinds of core splits structure are compared, and the critical design points are introduced.

The active core of a nuclear reactor splits atoms in two to produce bursts of energy and, as a byproduct, large masses of highly radioactive particles.

The four core classes aren't going anywhere but, as you've likely seen with Japanese destroyers and incoming Soviet destroyers, we're including "subclasses" by introducing splits in the tech tree.